Half Nut Repair

[restore49]

Bored out threads from Cincinnati half nut and will install new Spool Insert. Was hopping for a way to solder in with 60/40 solder and then maybe 4 1/16 roll pins. Will not be a lot of material on nuts when done machining (1/8" ) so looking for max strength. Will oven solder work? Bob

 

[TonyM]

How about flanging the new inserts for a belt and braces approach. Surely soft solder would then be enough. Plus easy to replace if you needed to redo in future

 

[petertha]

What did the original threaded half nuts look like?

Reason I ask is I would think there is a significant amount of thrust load acting on them during threading/power feeding (however your particular carriage is set up). The rotational screw-jack mechanical advantage is traversing your carriage against the cutting forces plus a bit of carriage friction.

On my 14x40 lathe the threaded 'clam shells' have a raised boss flange on either side which acts against the main casting. There are small pins/bolts located in the half nuts, but I think these are just to index them & prevent them from rotating out of position (=much smaller force).

 

[restore49]

Yes they will have a flange - should have explained that is what I meant by spool - like a spool of thread. Will also pin threw the flange to the original bronze casting - first picture. Would like to solder to give maximum strength - just not sure if soft flame will be enough and concerned about distortion.

 

[bazmak]

If the bearings are flanged and with a location pin then that should suffice,no need to solder etc Myford and others have been doing it that way for over 70 yrs without problems

 

[restore49]

The system Myford (which is what I will copy) and others use is good if you have a lot of material to work with. Have bored away half the thickness from the original nuts (second picture) to give me some wall thickness for the new insert (spool). My concern is epoxy will not give me as rigid an assembly as original . Just thinking solder would make the two parts stronger. looking for advise on how to solder - torch - oven - large iron?

 

[bazmak]

if the casting and the bobbin are both bronze then you can soft solder or silver solder or even braze. I would try silver solder but would be wary of distortion

 

[DJP]

Given the large contact area I think that soft solder is sufficient and sweating it like copper pipe plumbing with a propane torch would be my choice.

Silver soldering the flanges only is an alternative.

My thoughts for your consideration.

 

[Hopper]

I did a similar repair on my old Drummond lathe some years ago. Used the spool-shaped sleeve and soft soldered it in position. I tinned the half nut body and the half-spool piece with a thin layer of soft solder then put them together and heated until I could melt a bit more solder into the join for good measure. Has been working well for me for years since.

Between the large surface area of the soldered join and the definite location of the shoulder on the spool, it is plenty strong enough. If you've ever used a leadscrew with a hand wheel on the end as the old Drummonds and some Myfords do, you'll know the forces are not great. You turn the leadscrew handwheel with light finger pressure. Screwcutting would be a bit more pressure but light cuts so still not great.

 

[restore49]

Will try tinning - clamp and use toaster oven.

 

[restore49]

Success :thumbup:- thanks all for help. When tinning the pieces with plumbing torch everything was hot so just went for it and clamped and finished.

 

[bazmak]

as the old advert in the UK used to say, Success is assured if your showed
a copy of the highway code. Looks like you have done a great job
Now your the expert and can advise others.Nothing better than trial and error

 

[Hopper]

Well done! Should last you for many years.

 

[petertha]

Nice. Is the entire casting assembly bronze? If so, wow. You wont see that on a modern import.

 

[restore49]

Cincinnati Tray Top around 4 1/2 Lb. of Bronze. Think my next move is to swap the lead screw end to end.

 

[restore49]

Cut Lead screw flipped 180 - 1/4" pilot pin - 45 bevel - clamped on jigs - tack weld(more like root pass) - continuous weld.

 

[MRA]

That's really nicely done. Now, what about all that wear you're going to re-encounter down near the tailstock when you're cutting really long threads?

 

[bazmak]

If the leadscrew is concentric after welding then congratulations on being successful in doing something not many others would try

 

[restore49]

Was not concentric after welding - even though I did jig clamp it - .080 total run out. Used spot heat cool method ( with a little help hanging pipe over end) and got it down to .002 total with a little learned science. Lead screw was still ok but figured with new nut it deserved a clean area to work with. Just test fit and very happy with results. Once you cut screw into 3 pieces the rest is just time and patience. Bob

 

[MRA]

If you have a little time, I'd like to know more about how to use heat to move something beyond an elastic deflection (which might just relax back to where it started). Or - like you perhaps hint - was most of the action around the long bit of tube over the end?

(oh - and on further reflection, my joke above about long threads should more specifically have been around long LH threads. Just what are you going to do? ).